Industrial control systems comprise one or more controllers coupled with at least one Human Machine Interface (HMI) over a network or other communication system. The one or more controllers are linked to field devices or peripherals that gather data and perform control tasks—for example sensors, actuators, motors, console lights, switches, valves and contactors.
Control systems also include I/O devices which connect controllers to field devices, and which perform an interface function between the two. The input component of an I/O device may comprise one or more signal conditioning or signal conversion circuits, which enable conditioning and/or conversion of data signals received from a field device into logic signals capable of interpretation by the corresponding controller. The output component of an I/O device may comprise one or more signal conversion circuits configured to convert control signals from the controller into digital or analog signals that can be used to control various field devices.
Depending on type and model of a field device in use, corresponding input signals to, or output signals from such field device can vary significantly. Owing to limitations of existing technology, prior art control systems required a compatible I/O device to be selected and implemented for every different field device type or signal type.
FIG. 1A illustrates an exemplary control system 100 incorporating prior art I/O devices. Control system 100 includes human interface station (HIS) 102 which comprises an operator or user interface that is communicably coupled with field controls stations (FCS) 104 and 106. Each FCS comprises a controller that performs control computation functions for one or more function blocks within the control system, and which controls I/O functions for field devices.
In the illustration of FIG. 1A, FCS 104 includes field control unit (FCU) 108—which implements the control functions of FCS 104. FCS 104 additionally includes a plurality of node interface units (NIU) 110a to 110d. Each NIU 110a to 110d comprises an interface that communicates with and enables field control unit 108 to communicate with I/O devices (I/OD) 112a to 112c, and with field devices (FD) 114a or 114b that are connected to an NIU through such I/O device(s). The NIU may additionally include an interface that enables it to communicate with another NIU. It would be understood that FCS 106 may have a configuration similar to FCS 104.
As illustrated in FIG. 1A, each of NIU 110a, 110b and 110c are communicably coupled with I/O device 112a, 112b and 112c respectively. Of these, I/O devices 112a and 112b are respectively coupled with field device (FD) 114a and 114b. I/O device 112c remains available for coupling with a field device. Likewise, NIU 110d remains available for coupling with an I/O device and/or a corresponding field device.
Recent advances in I/O device technology have resulted in development of versatile I/O devices that are capable of interfacing with and processing I/O signal types. Stated differently, the new I/O devices accommodate multiple I/O signal types (and are therefore compatible with multiple field device types) and are capable of functioning as universal I/O and signal conditioners. Additionally, a single advanced I/O device of this type may be capable of being configured to simultaneously couple with one or more analog input field devices, analog output field devices, digital input field devices, and digital output field devices.
In one implementation, the recent I/O devices include multiple types of signal conditioners/converters on a single (or unified) baseplate, which enables flexible configuration and assignment of the I/O device so as to accommodate any one of a plurality of different field device types. These advanced I/O devices are also configured to have multiple I/O points, each I/O point being configured to function as an interface point for an I/O channel established between a field device and the I/O device.
The ability to bind multiple field devices to a single I/O device lowers the overall device footprint, and improves cost efficiencies. Additionally, the ability to flexibly bind a single I/O device type to multiple field device types results in significantly faster project completion without compromising quality. FIG. 1B illustrates an advanced I/O device (I/OD) 116 of the type described above—which I/OD 116 is communicably coupled to multiple field devices (FD) 118a to 118d. It would be understood that the total number of field devices that may be connected to a single I/O device of the type illustrated in FIG. 1B is limited by the maximum number of I/O points provided in the I/O device.
The availability of multiple I/O points in a single I/O device provides the ability to simultaneously establish multiple I/O channels, and additionally to combine multiple I/O channels into a single combined I/O channel, which combined I/O channel may be assigned or communicably connected to a field device. In an embodiment, the combination of multiple I/O channels may be achieved by configuring multiple I/O points within an advanced I/O device in a manner such that the individual I/O channels established at said multiple I/O points behave as a functionally combined I/O channel.
By way of example, multiple digital output channels of an I/O device may be combined into a single digital output channel to increase an output current delivered to a field device. In a more specific example, two single digital output channels, each respectively capable of carrying an output current of 0.67 amperes, may be combined to deliver an output current of approximately 1.3 amperes to a field device. In another example, three single digital output channels, each capable of carrying an output current of 0.67 amperes, may be combined to deliver an output current of approximately 2 amperes to a field device.
Similarly (i) multiple digital input channels associated with an I/O device may be combined into a single digital input channel (ii) multiple analog output channels associated with an I/O device may be combined into a single analog output channel and (iii) multiple analog input channels associated with an I/O device may be combined into a single analog input channel.
The ability to combine multiple channels established by an I/O device into a combined single I/O channel has presented a previously unanticipated difficulty in testing whether the I/O points associated with such combined channels have been appropriately configured, and whether the resulting combined channels are operating correctly.
Since a combined I/O channel comprises more than one individual component channel, conventional testing of a combined I/O channel requires testing of each component channel separately. FIG. 2 illustrates a flowchart setting out conventionally understood steps for ascertaining whether a combined I/O channel is operating correctly.
A combined I/O channel comprises a primary channel and one or more secondary channels. As illustrated in FIG. 2, conventional testing of a combined I/O channel involves at step 202, performing a signal check across the primary channel. Thereafter, step 204 comprises ascertaining whether any secondary channels associated with the primary channel remain to be tested, and if so, performing a signal check on the untested secondary channel at step 206. The method repeats steps 204 and 206 until signal checks have been completed on the primary channel as well as on all secondary channels associated with the combined I/O channel. Step 208 thereafter determines the status of the combined I/O channel based on results of testing of each of the primary and secondary channels.
The conventional testing method illustrated in FIG. 2 suffers from multiple drawbacks, including (i) requiring serialized testing and validation of signals on each of the primary and secondary channels—whereas ideally each of the primary and secondary channels should be tested concurrently, (ii) requiring manual comparison and analysis of anticipated signal values against measured values (iii) the signal testing is carried out manually, with the aid of physical sensors or measurement devices (such as a voltmeter, multimeter, ammeter or other sensing device) which is laborious and prone to human measurement and validation errors. Additionally, since this method relies on testing of individual I/O channels, the testing process can only be carried out after all channels between the I/O device and the concerned field device have been established (i.e. after the actual physical, wired or wireless connections have been established).
There is accordingly a need for an automated and accurate system for testing an I/O device configured to implement one or more combined I/O channels, which testing can be carried out even without establishing actual physical connections between the I/O device and the concerned field device.